Describe the 2 syntaxes HTML5 offers, what are some features that may make you chose one over the other.

I was not sure there were only 2 syntaxes HTML5 Offers, I thought syntax refers to the rules that specify the correct combined sequence of symbols that can be used to form a correctly structured program using a given programming language. This is on one of my practice quiz and I am confused. Please tell me if I am missing something here.